A conventional proximity sensor is applicable for a variety of automated machines, semiconductor equipment or machine tools. The proximity sensor senses an inducing element in a non-contacting manner so that data of the inducing element or of the position information of an operating mechanism is obtained by a controller. Referring to FIG. 1, a conventional inductive proximity sensor 10 contains a LC and transistor circuit to produce vibration, such that a sensing area A of a sensing end 11 of the inductive proximity sensor 10 generates a high-frequency electromagnetic field. When a magnetic metal object (such as iron or nickel) approaches a plane on a front end of a coil, a magnetic vortex in the induction coil changes to transform the circuit, thus outputting voltage. Thereafter, the inducing element is sensed if it moves close to or away from the coil.
The inductive proximity sensor 10 senses the inducing element made of magnetic metal material by using electromagnetic effects. Because magnetic lines of the coil are influenced by adjacent objects, when a magnetic attracting object or another magnetic proximity sensor approaches the inductive proximity sensor 10, a sensing error occurs to trigger the inductive proximity sensor 10. Taking a machine tool for example, when the machine tool machines a metal workpiece, metal chips attach in the sensing area A of the sensing end 11 of the inductive proximity sensor 10 to cause a sensing error and to trigger the inductive proximity sensor 10 accidently.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.